The present invention relates to a plasma process apparatus with in situ monitoring, a method for monitoring using the apparatus, and a method for cleaning a chamber used in the apparatus. More particularly, the present invention relates to in situ monitoring a plasma chamber using a sampling manifold connected to the chamber and a gas analyzer connected to the manifold, and includes a method for in situ monitoring a plasma process and a method for cleaning the plasma chamber after etching. In addition, the present invention relates to an optimized in situ cleaning method for removing residues inside a plasma chamber after etching polysilicon.
Generally, semiconductor device fabrication processes are carried out in processing chambers in which specific processing conditions, such as temperature and pressure, are preset and processing environments are created. In particular, a plasma process, such as a plasma etching process and a plasma enhanced chemical vapor deposition (PECVD) process, generates many by-products. These by-products react with gas, photoresist, or other materials present inside the processing chamber to create polymer materials. The polymer becomes attached to the wafer surface and the inside surfaces of the processing chamber, causing the processing parameters to deviate from the pre-set values, and generating particles. Particles cause wafer defects which result in a decrease in the productive yield of a semiconductor fabrication facility.
In order to reduce defects, preventive maintenance (PM) for the processing chamber is carried out on a certain schedule. Because the equipment can not be operated during PM, productivity is also reduced by frequent PM.
FIG. 1 shows the PM process for the conventional processing chamber. Equipment for a specific process of semiconductor fabrication, with a chamber requiring PM, is removed from operation, is powered off, has its vacuum released, and is allowed to cool down. When the processing chamber is sufficiently cooled down, the components of the processing chamber are disassembled. In the case of chambers used in plasma processes, the surfaces of each of the disassembled components are wet-etched to remove the by-products of plasma processing. The wet-etch normally uses chemicals in the hydrogen fluoride (HF) series in order to remove the polysilicon film or silicon nitride film. Then, after re-assembling the components, a vacuum pump is again operated to reestablish a vacuum, the power is turned on, and the equipment is brought on line. Test wafers are then loaded into the processing chamber of the equipment, and an aging process ensues. After aging, the test wafers are examined during Process Recertification, in order to check whether the processing chamber is ready for operational use.
However, the PM method described has some drawbacks. The method is expensive, wastes energy and takes a long time (over 24 hours).
In order to overcome the time problem, a plasma etch can be carried out using nitrogen trifluoride (NF3), or carbon tetrafluoride (CF4) instead of the wet etch. Alternatively, Thermal Shock Technology is employed to remove, by means of thermal stress, the films formed inside the chamber. In another alternative, a dry etch is performed using chlorine trifluoride (ClF3), or bromine pentafluoride (BrF5). Even with this alternative, the removal, the disassembly and the assembly are still required thereby resulting in the same economic losses and power waste.
In situ cleaning, without disassembly and assembly, for the processing chamber using dry etch gas has been introduced. However, it is difficult to measure the cleaning reaction precisely as it is being carried out and to determine the most efficient cleaning conditions. Thus, proper utilization of the in situ cleaning function is difficult, and optical utilization is unlikely.
The present invention is directed to an apparatus and methods which substantially overcomes one or more problems due to the limitations and the disadvantages of the related art.
An object of the present invention is to provide an apparatus and method for performing a plasma process with in situ monitoring, including performing a plasma etch process for the formation of polysilicon storage electrodes on a semiconductor wafer.
It is another object to provide an in situ cleaning process for a plasma chamber of the apparatus after the plasma etch process.
It is another object to optimize an in situ cleaning process based on results from monitoring a cleaning process in a plasma chamber.
To achieve these and other objects and advantages in accordance with the present invention, a plasma process apparatus with in situ monitoring includes a plasma chamber and a process gas supply in flow communication with the plasma chamber, for supplying a process gas to the plasma chamber. A waste gas discharge assembly is in flow communication with the plasma chamber for removing a waste gas resulting from a process performed in the plasma chamber, and includes a discharge pump. A sampling manifold is in flow communication with the plasma chamber. A sampling pump, in flow communication with the sampling manifold, induces flow of a sample gas from the plasma chamber through the manifold. A gas analyzer in flow communication with the manifold analyzes the sample gas flowing through the sampling manifold.
In another aspect of the present invention, the gas analyzer is a Residual Gas Analyzer-Quadropole Mass Spectrometer (RGA-QMS).
In another aspect of the present invention, an in situ monitoring method includes monitoring an initial gas in the plasma chamber, including inducing flow of the initial gas into the sampling manifold and analyzing the initial gas with the gas analyzer to measure background amounts of constituents. If the background amounts of the constituents exceed a contamination level, the plasma chamber and sampling manifold are baked to cause outgassing, and, after baking, the initial gas is again analyzed with the gas analyzer. A wafer is processed in the plasma chamber by supplying a process gas from the gas supply and a process reaction gas is produced. A process reaction is monitored by inducing flow of a process sample gas (which may include the process gas, the process reaction gas, or both) from the plasma chamber into the sampling manifold and analyzing the process sample gas with the gas analyzer. After the wafer is processed, it is unloaded, and a waste gas from the plasma chamber is discharged using the waste gas discharge assembly. The plasma chamber undergoes in situ cleaning in which a cleaning gas is supplied from the gas supply to the plasma chamber and a cleaning reaction gas is produced. A cleaning reaction is monitored by inducing flow of a cleaning sample gas (which may include the cleaning gas, the cleaning reaction gas, or both) from the plasma chamber into the sampling manifold and analyzing the cleaning sample gas with the gas analyzer.
In another aspect of the invention, an in situ cleaning method includes unloading the wafer after performing plasma etching of a polysilicon layer on a wafer in a plasma chamber. A cleaning gas is supplied from the gas supply to the plasma chamber at a set cleaning pressure and a set cleaning temperature. The cleaning gas includes a mixture of sulfur hexafluoride (SF6) gas and chlorine (Cl2) gas. The cleaning gas is supplied to separate, from inside the plasma chamber, a residue from the plasma process. The residue separated from the plasma chamber is then pumped out of the plasma chamber.
In another aspect of the invention, the cleaning method determines an optimized end point for the cleaning process. The cleaning pressure and cleaning temperature are reset to different values, after determining a cleaning process end point. Then a combination of the cleaning temperature and the cleaning pressure associated with a minimum cleaning process end point is identified. Then the next wafer is plasma etched, and thus the process is repeated. After several repetitions, the combination provides conditions for optimal cleaning.
Therefore, according to the present invention, a plasma etch process for the formation of polysilicon storage electrodes of semiconductor capacitors is monitored using the sampling manifold and the gas analyzer, and the cleaning process is also precisely monitored in situ in the process chamber, thereby allowing the recipe for the cleaning process to be optimized and improving the efficiency of semiconductor manufacturing using the plasma chamber.